Mechanical response and plastic deformation of coherent twin boundary with perfect and defective structures

L Zhang and W Mao and M Liu and Y Shibuta, MECHANICS OF MATERIALS, 141, 103266 (2020).

DOI: 10.1016/j.mechmat.2019.103266

Coherent twin boundary (CTB) is an important structural defect, which is generally considered to have a perfect structure in the previous theoretical and computational studies. However, the CTBs observed in the recent experimental research in the submicrometer range were found to have inherent imperfections. In this work, we investigated the difference between perfect and defective CTB structures in mechanical responses and deformation mechanisms using molecular dynamics simulations. Two typical defective CTB structures with either incoherent twin boundary (ITS) step or self-interstitial atoms (SIA) cluster were considered. The simulation samples were deformed under uniaxial strain in different directions and were deformed under shear strain. Compare to the CTB with perfect structure, the stability of the defective CTB decreased significantly, and the simulated samples softened due to the existence of the ITB step and SIA cluster. When the critical stress was reached, the first dislocations were nucleated in the crystal lattice of the bicrystal sample with a perfect CTB structure. However, the CTB with structural defects played a role as the dislocation source to release dislocations, thus reducing the yield stress. Under uniaxial tension and compression, the yield stress of CTB with the SIA cluster was lower than that of CTB with ITB step in all simulated conditions. Dislocation analysis indicated that the difference was ascribed to the dissociation of an existed Frank dislocation loop on the twin plane rather than the nucleation of new dislocations from the CTB/ITB junction. Under shear deformation, the shear strain separated the structural defects from the CTB plane and transformed the defective CTB structure into a single perfect CTB. The simulation results provide a better understanding of the mechanical properties and deformation mechanisms of CTB-strengthened materials.

Return to Publications page